Cassette film transport

ABSTRACT

Automatic filmer capable of centering the cassette with respect to an x-ray window and measuring the width and length thereof. Oppositely disposed channels are used to center the cassette about a first center line and measure the width thereof. A gripper assembly is used to draw the cassette into the housing and determine the length of the cassette. A carriage assembly moves the cassette within the housing so as to expose the cassette to x-rays within the x-ray window.

BACKGROUND OF THE INVENTION

The present invention is directed to a method and apparatus forautomatically receiving an x-ray film cassette and moving the x-ray filmcassette within an x-ray apparatus for exposure.

There exists a large variety of sizes of x-ray film cassettes that areused to obtain x-ray pictures. Generally, these cassettes aresubstantially rectangular in shape and may be placed in one of twodirections within an x-ray machine for exposure. Generally some type ofmechanism is provided for placing the cassette within the x-ray window.In addition to being able to accommodate a variety of different sizedand shaped cassettes, many x-ray devices of the prior art are capable oftaking x-rays in the tomographic mode. With regard to x-ray machinesthat take x-rays in the tomographic mode it may also be necessary toprovide a transport system for moving the cassette in the x-ray window.When used in the tomographic mode care must be taken so as to accuratelymove the cassette.

Applicant's invention provides an improved method and apparatus forreceiving the transporting an x-ray cassette within an x-ray apparatusfor both fixed and tomographic x-rays.

SUMMARY OF THE INVENTION

In one aspect of the present invention there is provided an automaticx-ray cassette filmer comprising a housing having an opening therein forplacement of an x-ray film cassette. The housing is provided with meansfor securely holding the x-ray cassette and moving the cassette eitherin or out of the housing. Carriage means are also provided for movingand aligning the cassette with an x-ray window.

In another aspect of the present invention there is provided a methodfor automatically receiving and centering an x-ray film cassette in anx-ray apparatus comprising the steps of: placing an x-ray cassette in anopening in the apparatus designed for receiving the cassette until itcontacts a rear stop; centering the cassette about a first horizontalcenter line; centering the cassette within the housing about a secondhorizontal line so that it aligns the cassette with one axis of thex-ray window; moving the cassette upon receiving appropriate signal intoa position in the x-ray window so as to allow exposure of the filmcassette.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus for taking x-raysincorporating the automatic filmer made in accordance with the presentinvention;

FIG. 2 is a bottom view of the automatic filmer within the housing astaken along line 2--2 of FIG. 1;

FIG. 3 is a perspective view of the gripper assembly of the automaticfilmer made in accordance with the present invention;

FIG. 4 is a bottom perspective view of the carriage assembly whichcarries the gripper assembly of FIG. 3;

FIGS. 5 A-I illustrate in diagrammatical form the various stages ofmovement of an x-ray film cassette placed within the automatic filmer ofFIG. 1;

FIG. 6 is a side cross-sectional view of the gripper assembly of FIG. 3taken along line 6--6;

FIG. 7 is a top view of the channel assembly of the automatic filmer ofFIG. 1 which is mounted to the carriage assembly of FIG. 3;

FIG. 8 is a perspective view of the drive mechanism used to move gripperassembly of FIG. 6; and

FIG. 9 is an enlarged cross-sectional view of the drive pin of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2 there is illustrated an x-ray apparatus 10having automatic filmer 12 made in accordance with the presentinvention. The x-ray apparatus comprises a patient support surface 13which is slidably mounted on the filmer cassette housing 14. In theparticular embodiment illustrated, the filmer cassette housing 14 ispivotably mounted to the main body frame 16 by rotatable shaft (notshown). In the particular embodiment illustrated the x-ray apparatus 10is capable of providing tomographic x-rays. A rotatable tomo arm 20 isprovided for moving an x-ray source 22 for operation of the apparatus inthe tomograhic mode. The filmer cassette housing 14 has disposed thereinan automatic filmer mechanism 12 made in accordance with the presentinvention. The housing 14 is provided with an opening 21 for receivingor ejecting an x-ray film cassette 28 (see FIGS. 5A-I and FIG. 6). Theopening, if desired, may be provided with a gate assembly (not shown)for allowing or preventing entry therein. A gate assembly such asdisclosed in co-pending application, Ser. No. 07/044725 filedsimultaneously herewith could be employed, and such application ishereby incorporated herein.

The automatic filmer 12 is provided with a carriage assembly 30 which ismounted within the housing 14 so that it can be moved in the axialdirection for placement of a film cassette 28 within the x-ray window29. In the particular embodiment illustrated one side of carriageassembly 30 is slidably secured to a guide rod 31. The carriage assembly30 is driven along guide rod 31 by timing belt 33 attached thereto. Thebelt 33 is wrapped around drive pulley 34 which is driven by a motor 35through pulley 37 connected to motor 35, belt 38 on pulley 37 and pulley39 which is directly connected to pulley 34. The opposite side ofcarriage assembly 30 has a pair of rollers 36 which ride on housing 14.By rotating pulley 34 in the appropriate direction carriage assembly 30is moved toward or away from x-ray window 29. The x-ray cassette 28 mayoccupy a stationary position in the x-ray window or be moved within thex-ray window so as to provide tomograhic x-rays.

When an x-ray film cassette 28 is placed through opening 21 it engages agripper assembly 40 (see FIG. 4) which is slidably mounted on carriageassembly 30. In the particular embodiment illustrated, gripper assemblyis provided with rollers 41 which roll along linear guide rails 43 ofcarriage assembly 30.

Referring to FIG. 6 there is illustrated a cross-sectional side view ofthe gripper assembly 40. The gripper assembly 40 includes a base plate42 having an upper surface 44 and lower surface 46. Secured to uppersurface 44 of plate 42 is a bearing block 48 having supporting pin 50pivotably affixed thereto. An upper jaw 52 is mounted to pin 50. Atorsion spring 54 biases the upper jaw 52 downward toward plate 42. Theother end of the upper jaw 52 extends through an opening 56 in plate 42and is connected to lower jaw assembly 58 which is securely attached tolower surface 46 of plate 42 by lower bearing block 60. Lower bearingblock 60 includes a pin 62 which is capable of being rotated therein. Alower jaw 64 is attached to pin 62 so that lower jaw 64 will rotate aspin 62 is rotated. Lower jaw 64 is normally biased toward the upper jaw52 by spring means 70. Spring means 70 comprises a coil spring which isconnected to plate 42 at one end and the other end is attached to pin 62by connecting member 61. Connecting member 61 is attached to pin 62 sothat it rotates as pin 62 is rotated. The spring 70 is affixed to theplate 42 by attachment means 72. In the particular embodimentillustrated the attachment means 72 is a screw which threadedly engageslower surface 46 of plate 42. A cam follower 73 is affixed to lower arm74 in such a manner that pin 62 rotates about its axis as rollerfollower 73 is forced down cam ramp 76. A push/pull rod 75 is pivotablyconnected to lower jaw 64 by pin 77. The other end of push/pull rod 75is connected to lower end 79 of upper jaw 52 by adjustable screw means80. A cam ramp 76 is attached to the carriage assembly 30 (not shown inFIG. 6).

FIG. 6 illustrates the gripper assembly 40 in the receiving position. Inthis position the roller follower 74 has been forced down cam ramp 76 soas to cause the lower jaw 64 to be moved away from plate 42 and theupper jaw 52 caused to move away from the lower jaw by adjustablepush/pull rod 75. Push/pull rod 75 is adjusted so that it will moveupper jaw 52 away from plate 42 as cam follower 73 rides down cam ramp76 and moves upper jaw 52 toward plate 42 as it rides up cam ramp 76.Accordingly, as gripper assembly 40 moves away from its receivingposition the roller 74 will ride up ramp 76 thereby allowing the upperjaw 52 and lower jaw 64 to firmly grip the end of the cassette. Thecassette 28 is illustrated in the dashed lines. As the cassette 28 ispushed in engagement with the upper bearing block 48 a switch 82disposed within bearing block 48 is depressed thereby causing activationof a drive means which causes gripper assembly to move away from camramp 76. As the roller follower 74 rides up cam ramp 76 the lower jawand upper jaw 52, 64 respectively begin to securely hold the cassette 46therebetween. Likewise, when the gripper assembly is brought intoreceiving position roller 73 will ride down ramp 76 thereby causing theupper jaw and lower jaw to release the cassette therefrom.

Referring to FIG. 5A-5I there is diagrammatically illustrated the stepsin which the cassette is received in housing 14 and transferred to thex-ray window 29 and then ejected from the housing 14. FIG. 5Aillustrates an x-ray film cassette 28 about to be passed through opening21 in housing 14. The x-ray cassette 28 is passed through an optionalgate assembly (not shown) in either one two orientations. This breaks ascanner beam and locks out all electronics not involved with themovement of the cassette 28. The cassette 28 is passed through opening21 until it contacts bearing block 48. At this point motor-driven guidechannels which form a part of the carriage assembly 30 converge on thecassette 28 from both sides (see FIG. 5C) so that the vertical centerline 86 of the cassette 28 aligns center line 87 of opening 21.

Referring to FIG. 7 there is illustrated a channel assembly 81 used tocenter the cassette along center line 87 of channel assembly 81. Thechannel assembly 81 comprises a pair of substantially "C" shapedchannels 91. The open end of each channel 91 faces toward the centerline 87. The channels 91 are supported by threaded screws 92, one ateach end of channel 91. The channels 91 each have a nut 93 at theleading end attached rigidly to and below the channel 91 to allow thecassette to slide into the channel, while the nut 94 (shown in dashlines) on the trailing end 95 of channel 91 is confined by the channeland allowed to float to minimize alignment problems. The screws 92 aresupported by self aligning bearings 96 secured to carriage assembly 30.Self aligning bearings 96 allow the screws 92 to turn freely in spite ofany inaccuracies in forming of the carriage assembly to which thebearings are attached. The left side 97 of screws 92 are provided withleft handed threads while the right side 98 are provided with righthanded threads so that the channels 91 may be moved toward or away fromeach other by rotating the screws. The screws 92 are linked together bya cable chain 99 so that they turn in a 1:1 ratio. Screw 92 has a drivecoupling 100 which engages a pulley 101 which is driven by drive channelpulley 102 driven by a drive motor 103. Drive motor 103 may turn ineither direction and has an encoder 104 attached thereto which countsthe revolutions of the motor. This information is related to themicroprocessor and is used to determined the position of channels 91.Accordingly, the width of the cassette can be readily calculated by themicroprocessor. A microswitch 105 is disposed within each channel 91 tosense when a cassette is present.

When a cassette 28 is inserted into gripper assembly 40 a signal isgiven to start the channel drive motor 103. The channels 91 advancetoward the cassette 28 on both sides at equal speed, causing the centerline of the cassette to move toward the center line 87 of the channelassembly 81, regardless of the size of the cassette 28. When a signal isreceived from both of the two limit switches 105 built into thechannels, indicating that both channels have contacted cassette 28,which is now centered, channel drive motor 103 will stop. The channeldrive motor 103 will reverse briefly to withdraw the channels 91 fromthe cassette 28 tightly. The gripper assembly 40 then draws the cassette28 into the housing be sliding it between channels 91 which act as guidesurfaces, until the cassette is centered on the longitudinal center line90.

The drive assembly consisting of motor 103, encoder 104, pulleys 102 and101 is attached securely to housing 14 and does not move with carriageassembly 30 when this carriage transports the x-ray cassette to thefilming position. The drive coupling 100 has a pair of drive pins 106which disengage from drive slots in pulley 101 when carriage assembly 30moves to the filming position. These pins are spring biased so in theevent that the pins 106 of drive coupling 100 do not align with thedrive slots in pulley 101 when the carriage assembly returns to the homeposition, the pins will nevertheless snap into the appropriate holes inpulley 101 when this pulley is turned by the channel drive motor 103.

After the center line 86 (channel drive) of cassette 28 has been alignedwith center line 87 of channel assembly 81, the cassette 28 is drawnwithin the housing 14. The operator continues to hold pressure againstthe cassette 28 until the cassette 28 begins to be automatically drawninto the housing (see FIGS. 5C and 5D). The operator may release thecassette when the gripper assembly 40 has firmly clamped the cassette 28between upper jaw 52 and lower jaw 64. Cassette 28 will continue to bedrawn into the housing 14 until the cassette's longitudinal center line89 is aligned with the longitudinal center line 90 of the x-ray window29 (see FIGS. 5D and 5E). FIG. 5E illustrates the "home" position. Uponreceiving a signal from the operator, the cassette 28 will move rapidlyto a position centered at the x-ray window 29 (FIG. 5F) at which pointan x-ray picture may be taken. If so desired, the cassette 28 may bemoved in synchronism with a tomographic arm (FIG. 5G) in order to take atomographic x-ray picture as is more fully described in a co-pendingapplication, Ser. No. 07/044643, now U.S. Pat. No. 4,754,471, which wasfiled simultaneously with this application and is hereby incorporated byreference. Upon receiving a signal that the x-ray film has been exposed,the cassette 28 returns to the home position illustrated in FIG. 5H.After reaching the home position the cassette 28 is automaticallyejected from the housing 14 and stops at a position from which it can beremoved by the operator (FIG. 5I).

Referring back to FIG. 2, a counterweight carriage assembly 110 ismounted to move in linear relation to the filmer housing 14 by means ofrollers 114 which roll along linear guide rails 115 attached to housing14. The counterweight carriage assembly is linked to the filmer carriageassembly 30 by timing belt 33. The counterweight carriage assembly 110includes a pulley 112 mounted to housing 14 around which timing belt 33is placed. The other end of timing belt 33 is driven by pulley 34 whichalso drives carriage assembly 30. A counterweight 116 of appropriateweight is incorporated into the carriage 110, which is attached totiming belt 33 so that it moves in the opposite direction from whichcarriage assembly 30 moves. Counterweight carriage assembly 110 reducesthe power required to move the carriage assembly 30 when the patientsupport surface 13 is disposed in the substantially vertical position.The counterweight carriage assembly 110 also assists in smoothing outthe movement of carriage assembly 30 for all positions of the patientsupport surface 13.

Referring to FIGS. 4 and 8, there is illustrated the drive mechanism 120for moving the gripper assembly 40. Drive mechanism 120 is locatedwithin housing 14 below the home position of carriage assembly 30. Themounting of drive mechanism 120 is totally independent of gripperassembly 40 and carriage assembly 30. On the bottom side of gripperassembly 40 (see FIG. 4) there is provided a drive plate 121 which has adrive slot 122. When the carriage assembly is in the home position driveslot 122 engages a spring loaded drive pin 123. Drive pin 123 is themeans be which gripper assembly 40 is moved, causing cassette 28 to bedrawn into or out of the housing 14. When carriage assembly 30 moves tothe position within the x-ray window in order for an x-ray picture to bereceived, drive plate 121 disengages from drive pin 123. This eliminatesthe need for the drive unit for the gripper assembly to move withcarriage 40. The drive slot 122 has angled edges 126 that get wider asthey approach outer peripheral edge 125 of the drive plate to makereengagement of the drive plate 121 with the pin 123 when the carriage30 returns to the home position less critical.

The drive pin 123 is mounted to a drive block 126 which is slidablymounted on guide rod 128. A drive screw 130 is securely attached bybearings to mounting blocks 131 at its ends which are secured to housing14. The drive screw 130 is connected to the drive block 126 by drive nut132. As the drive screw 130 is rotated, it causes the drive nut 132 tomove along the drive screw 130 and thus moves the drive pin 123 alongthe axis of the guide rod 128. The drive screw 130 is appropriatelyturned by a drive motor 135 by belt 137 and pulleys 139, 141. An encoder136 attached to motor 135 for determining the position of the drive pin123 along drive screw 130. The encoder 136 counts the number ofrevolutions of the motor and thereby translates this to the position ofthe drive pin 123 along the guide rod 128.

Referring to FIG. 9 there is shown an enlarged cross-sectional view ofthe drive pin 123 of FIG. 8. The drive pin 123 comprises a plastic pin143 which may slide up and down in pin housing 138. The travel of thepin 143 is limited by a limiting pin 140 which extends through slot 142in housing 138. The limiting pin 140 limits the vertical movement of thedrive pin 123. A spring 145 is disposed beneath the drive pin 123 whichforces it upward so it is normally positioned at the upper limit of itstravel range. The top of the drive pin is beveled so it meshes smoothlywith the angled edges 126 of the drive plate 121. The drive motor 135controls the position of the drive pin 123, which in turn controls theposition of the gripper assembly 40. The encoder 136 built into thesmall motor 135 allows the position of the gripper assembly 40 to bedetermined at all times. Thus the position of the leading edge ofcassette 28 is also known. Sensing means is also provided fordetermining the trailing edge of cassette 28. In the particularembodiment illustrated a light source 151 (see FIG. 5A) is positionedwithin housing 14 behind opening 21, preferably in line with center line87. The sensor 150 senses when the trailing edge of the cassette 28 haspassed. This information along with the information from encoder 136 isused in centering the cassette and determining its size for the purposeof adjusting x-ray image size.

Should pin 123 ever become disengaged in the home position, the pin 123travels toward the gripper assembly 40 until it strikes the angledperipheral edges 125 of the drive plate 121 which causes drive pin 123to ride down in housing 138, and because it is spring loaded it willreengage slot 122.

It is to be understood that various changes and modifications may bemade without departing from the scope of the present invention.

What is claimed is:
 1. An automatic x-ray cassette filmer comprising ahousing having an opening therein for placement of an x-ray filmcassette therethrough, means for receiving or dispensing said filmcassette through said opening, and for securely holding said filmcassette when said cassette is within said housing, an x-ray window, andcarriage means for moving said cassette in a direction so that saidcassette will align with said x-ray window, said means for receiving andholding said cassette comprising a gripper assembly having an upper jawand a lower jaw for clampingly holding said cassette, wherein saidgripper assembly is provided camming means for releasing said upper andlower jaws from clamping engagement with said cassette, said cammingmeans comprising a cam ramp secured to said carriage means and a camfollower secured to said gripper assembly such that when said camfollower engages said cam ramp said upper and lower jaws disengage saidcassette.
 2. An apparatus according to claim 1 further comprising drivemeans secured to said housing for moving said gripper assembly alongsaid carriage means, said drive means comprising a drive pin slidablymounted on a guide rod which is secured to said housing by anchorblocks, means for moving said pin along said guide rod, and means forreleasably engaging said pin with said gripper assembly.
 3. An apparatusaccording to claim 2 wherein said apparatus further comprises controlmeans for controlling the operation of said apparatus, said means forreleasably engaging said pin with said gripper assembly comprises adrive plate secured to the bottom side of said gripper assembly, saiddrive plate having a slot capable of receiving said drive pin, said slothaving a pair of oppositely disposed sides oriented such that they havea wide mouth which narrows down to a narrower portion for engaging saiddrive pin, said drive means having means for locating the position ofsaid drive pin and relaying this information to the control means ofsaid apparatus.
 4. An apparatus according to claim 1 wherein saidgripper assembly further comprises a mounting plate having an uppersurface and bottom surface, the upper surface of said mounting platehaving a first bearing block or blocks secured thereto, said firstbearing block or blocks having a pin rotatably mounted at the upper endthereof, said upper jaw being secured to said pin, said upper jaw havingits lower end extending through an opening in said plate, the lowersurface of said plate having a lower bearing block or blocks securedthereto, said lower bearing block or blocks having a second pinrotatably mounted therein, said lower jaw being allocated to said secondpin, a cam follower on an arm being also attached to said second pin forengagement with said cam ramp secured to said carriage, said second pinhaving a plate secured thereto for rotation with said pin, said platehaving a portion extending away from said pin, said portion having anopening therein which is secured to one end of a spring, the other endof said spring being connected to said plate for biasing said pin andlower jaw toward said cassette, when said cam follower engages said camramp it causes said lower jaw to disengage said cassette, means areprovided for connecting said lower jaw to said upper jaw such that saidupper jaw and lower jaw will move away from each other when said camfollower engages said cam ramp.
 5. An apparatus according to claim 3wherein said drive pin is held in a pin housing secured to a mountingblock; disposed within said pin housing is a limiting pin which extendsthrough an opening in said pin housing for limiting the movement of saiddrive pin; disposed beneath said drive pin is a spring for biasing thedrive pin upwards, the upper end of said engaging pin having a bevelededge.
 6. An apparatus according to claim 4 wherein said first bearingblock includes a switch which upon engagement with a cassette causessaid drive motor of said drive pin to move in a first direction.
 7. Anx-ray filmer apparatus comprising:movable carriage means movable along afirst path for moving an x-ray film cassette between a loading stationand an x-ray station; drive means coupled to said carriage means fordriving said carriage means in a first direction from said loadingstation to said x-ray station and in a second direction from said x-raystation to said loading station; and a counterweight assembly coupled tosaid drive means so as to move in a direction opposed to said directionof movement of said carriage means.
 8. An apparatus for automaticallypositioning an x-ray film cassette comprising:a housing; a slot in saidhousing through which the x-ray film cassette is receivable, a leadingedge first; gripping means movable within said housing to a firstposition near said slot for gripping the cassette at only a regionadjacent the leading edge of the cassette as the cassette is receivedthrough said slot; and drive means for moving said gripping means awayfrom said slot to a second position such that upon energization thereof,the x-ray film cassette is caused to be pulled at only a region adjacentits leading edge through said slot and into said housing.
 9. Theapparatus of claim 8 further comprising:means responsive to presence ofthe cassette leading edge adjacent said gripping means for energizingsaid drive means.
 10. The apparatus of claim 8 further comprising:meansassociated with said gripping means for preventing said gripping meansfrom gripping the cassette at the region adjacent leading edge when saidgripping means is at said first position such that as said grippingmeans moves from said first position towards said second position, saidgripping means grips at only a region adjacent the leading edge of thecassette wherein to pull the cassette into said housing.
 11. Theapparatus of claim 10 further comprising:means responsive to presence ofthe cassette leading edge adjacent said gripping means for energizingsaid drive means wherein to move said gripping means from said firstposition.
 12. The apparatus of claim 8 further comprising:a pair ofmovable side rails within said housing and defining therebetween avariable-width cassette receiving area aligned with said slot, said siderails being movable toward and away from each other wherein to move saidrails into and out of engagement with a cassette received through saidslot; second drive means associated with said rails for simultaneouslymoving said rails toward each other until each said rail comes intoengagement with the cassette wherein to align the cassette in said slot.13. The apparatus of claim 12 further comprising:means responsive topresence of the cassette leading edge adjacent said gripping means forenergizing each of said drive means.
 14. The apparatus of claim 12wherein each said side rail extends in a direction from said slot toengage sides of the cassette along the width thereof and perpendicularthe leading edge, the apparatus further comprising:means associated withsaid side rails for determining the width of said cassette receivingarea wherein to determine the width of the cassette upon engagement ofthe sides thereof by said rails.
 15. The apparatus of claim 12 furthercomprising:third drive means for collectively moving said gripping meansand said rails between a cassette-receiving position aligned with saidslot and an x-ray position offset from said slot.
 16. An apparatus forautomatically positioning an x-ray film cassette comprising:a housing; aslot in said housing through which the x-ray film cassette isreceivable, a leading edge first; gripping means movable within saidhousing to a first position near said slot for gripping at a regionadjacent the leading edge of the cassette as the cassette is receivedthrough said slot; drive means for moving said gripping means away fromsaid slot to a second position such that upon energization thereof, thex-ray film cassette is caused to be pulled at a region adjacent itsleading edge through said slot and into said housing; second drive meansfor selectively moving said gripping means between said second positionand a third position wherein to move the cassette into position forx-ray reception; and interconnect means for selectively connecting saidfirst mentioned drive means to said gripping means, said first drivemeans being connected to said gripping means when said gripping means isbetween said first and second positions, said first drive means beingdisconnected from said gripping means when said gripping means isbetween said second and third positions.
 17. The apparatus of claim 16,said interconnect means including:a movable drive pin associated withsaid first drive means; and a drive plate associated with said grippingmeans, said drive plate including slot means for selectively engagingsaid drive pin wherein to move said drive plate with said drive pin,said drive pin being engaged by said slot when said gripping means isbetween said first and second positions, and said drive pin beingdisengaged from said slot means when said gripping means is between saidsecond and third positions.
 18. An apparatus for automaticallypositioning an x-ray film cassette comprising:a housing; a slot in saidhousing through which the x-ray film cassette is receivable, a leadingedge first; gripping means movable within said housing to a firstposition near said slot for gripping at a region adjacent the leadingedge of the cassette as the cassette is received through said slot;drive means for moving said gripping means away from said slot to asecond position such that upon energization thereof, the x-ray filmcassette is caused to be pulled at a region adjacent its leading edgethrough said slot and into said housing; a pair of movable side railswithin said housing and defining therebetween a variable-width cassettereceiving area aligned with said slot, said side rails being movabletoward and away from each other wherein to move said rails into and outof engagement with a cassette received through said slot; second drivemeans associated with said rails for simultaneously moving said railstoward each other until each said rail comes into engagement with thecassette wherein to align the cassette in said slot; third drive meansfor collectively moving said gripping means and said rails between acassette-receiving position aligned with said slot and an x-ray positionoffset from said slot; lock out means for preventing said third drivemeans from moving said gripping means and said rails until said grippingmeans has pulled the cassette into said housing.
 19. An apparatus forautomatically positioning an x-ray film cassette comprising:a housing; aslot in said housing through which the x-ray film cassette isreceivable, a leading edge first; gripping means movable within saidhousing to a first position near said slot for gripping at a regionadjacent the leading edge of the cassette as the cassette is receivedthrough said slot; drive means for moving said gripping means away fromsaid slot to a second position such that upon energization thereof, thex-ray film cassette is caused to be pulled at a region adjacent itsleading edge through said slot and into said housing; a pair of movableside rails within said housing and defining therebetween avariable-width cassette receiving area aligned with said slot, said siderails being movable toward and away from each other wherein to move saidrails into and out of engagement with a cassette received through saidslot; second drive means associated with said rails for simultaneouslymoving said rails toward each other until each said rail comes intoengagement with the cassette wherein to align the cassette in said slot;third drive means for collectively moving said gripping means and saidrails between a cassette-receiving position aligned with said slot andan x-ray position offset from said slot; a motor; and drive couplingmeans for selectively connecting said motor to said second drive means,said motor being connected to said second driving means when said railsare in said cassette receiving position, said motor being disconnectedfrom said second driving means when said rails are in said x-rayposition.
 20. The apparatus of claim 19 further comprising:interconnectmeans for selectively connecting said first mentioned drive means tosaid gripping means, said first drive means being connected to saidgripping means when said gripping means is between said first and secondpositions, said first drive means being disconnected from said grippingmeans when said gripping means is between said cassette-receiving andx-ray positions.
 21. The apparatus of claim 20, said interconnect meansincluding:a movable drive pin associated with said first drive means;and a drive plate associated with said gripping means, said drive plateincluding slot means for selectively engaging said drive pin wherein tomove said drive plate with said drive pin, said drive pin being engagedby said slot means when said gripping means is between said first andsecond positions, and said drive pin being disengaged from said drivepin when said gripping means is between said cassette-receiving andx-ray positions.
 22. An apparatus for automatically positioning an x-rayfilm cassette comprising:a housing; at least first and second opposededges defining a slot in said housing through which the x-ray filmcassette is receivable, a leading edge first; a support movable withinsaid housing to a first position near said slot; a first jaw mounted tosaid support, said first jaw being adjacent said first edge when saidsupport is at said first position; a second jaw mounted to said support,said second jaw being adjacent said second edge when said support is atsaid first position, said jaws being movable toward each other to gripat only a region adjacent the leading edge of the cassette therebetweenas the cassette is received through said slot; and drive means formoving said support to a second position spaced from said slot such thatupon energization thereof, the x-ray film cassette is caused to bepulled at only a region adjacent its leading edge through said slot andinto said housing.
 23. The apparatus of claim 22 furthercomprising:means responsive to presence of the cassette leading edgebetween said jaws for energizing said drive means.
 24. The apparatus ofclaim 22 further comprising:jaw control means for moving said jawstoward each other wherein to grip the cassette and pull the cassetteinto said housing as said support moves from said first position to saidsecond position.
 25. An apparatus for automatically positioning an x-rayfilm cassette comprising:a housing; at least first and second opposededges defining a slot in said housing through which the x-ray filmcassette is receivable, a leading edge first; a support movable withinsaid housing to a first position near said slot; a first jaw mounted tosaid support, said first jaw being adjacent said first edge when saidsupport is at said first position; a second jaw mounted to said support,said second jaw being adjacent said second edge when said support is atsaid first position, said jaws being movable toward each other to gripat a region adjacent the leading edge of the cassette therebetween asthe cassette is received through said slot; drive means for moving saidsupport to a second position spaced from said slot such that uponenergization thereof, the x-ray film cassette is caused to be pulled ata region adjacent its leading edge through said slot and into saidhousing; jaw control means for moving said jaws toward each otherwherein to grip the cassette and pull the cassette into said housing assaid support moves from said first position to said second position,said jaw control means including:a cam ramp adjacent said support firstposition; and a cam follower coupled to said jaws and movable with saidsupport, said cam follower positioned to ride said cam ramp such thatsaid jaws are caused to move toward each other as said support movesfrom said first position toward said second position.
 26. A method ofautomatically positioning an x-ray film cassette comprising:inserting aleading edge of an x-ray film cassette through a slot in an x-ray filmhousing; gripping the cassette at only a region adjacent the leadingedge of the cassette as it is inserted through the slot; and pullingsaid cassette into the housing at only a region adjacent the leadingedge.
 27. The method of claim 26 wherein the cassette is pulled into thehousing to a home position with the assistance of a drive mechanism, themethod further comprising:moving the cassette to an x-ray position afterthe cassette has been pulled to said home position wherein the drivemechanism is not moved with the cassette when the cassette is movedbetween said home and x-ray positions.
 28. The method of claim 26further comprising:moving the cassette to an x-ray window after thecassette has been pulled into the housing; and moving the cassettewithin the x-ray window so as to provide a tomographic x-ray.
 29. Themethod of claim 26 further comprising: aligning the cassette in the slotas the cassette leading edge is inserted through the slot.
 30. Themethod of claim 29 wherein the cassette is pulled into the housing to ahome position with the assistance of a first drive mechanism and thecassette is aligned in the slot with the assistance of a second drivemechanism, the method further comprising:moving the cassette to an x-rayposition after the cassette has been pulled to said home positionwherein the drive mechanisms are not moved with the cassette when thecassette is moved between said home and x-ray positions.